This invention relates to diaphragms for use in acoustic instruments. More particularly, this invention relates to a diaphragm comprising a shaped body of a composite material consisting essentially of a thermoplastic resin such as polyvinyl chloride resin and graphite powder, and a method of producing the same.
Diaphragms for acoustic instruments, particularly diaphragms for speakers and microphones are required to have light weight, high rigidity and a high specific modulus of elasticity E/.rho., wherein E is Young's modulus and .rho. is the density, so that the diaphragms may efficiently reproduce acoustic signals over a wide frequency range with a high fidelity.
For this reason, wood pulp, plastics, aluminum, titanium and other materials have previously been used to form diaphragms. These materials, however, do not fully meet the above-mentioned requirements.
Synthetic resins have also been used in the manufacture of diaphragms. Examples include composite materials of carbon fiber and a synthetic resin. These composite materials, however, cannot provide sufficient rigidity when molded into a diaphragm shape partly because of insufficient integration of the resin attributable to the lubricating nature of the carbon fiber surface.
Boron, beryllium and carbon are known as having a high specific modulus. These materials have poor processing characteristics, which increase costs for molding them into diaphragms.